The invention concerns a sorter with a symmetric screen which is arranged concentrically in an essentially symmetric housing. In the interior of the housing there is concentrically contained a rotor drum featuring on its outer circumference sorting elements that sweep across the screen and circulate at least parts of the suspension being sorted around the walls of the drum. The sorting elements have a design such that they generate a vortex flow of the suspension in the housing. The housing features on its periphery at least a removal duct for heavy contaminants, and in one of its end walls a central lightweight dirt drain.
A sorter of that type is known from DE-C 25 48 578. On this sorter, the drum supports the sorting elements, which are installed in the screen space formed between the drum and the screen concentrically surrounding it. The drum and the sorting elements are part of the rotor, the axis of rotation of which essentially coincides with the longitudinal axis of the screen basket, which at the same time also is the axis of rotational symmetry of the screen basket. This arrangement creates a recirculation of the suspension--preferably fiber suspension in the waste paper industry--between screen space and drum interior, that is, practically around the walls of the drum. This is meant to improve the separation of contaminants. In this described arrangement, the removal space for the heavy contaminants borders on the housing area which accommodates the screen and the drum and is relatively narrow, the outside diameter of the housing being considerably larger than the largest inside diameter of the cylindrical screen. The lightweight contaminants are removed from the central, axial area of the housing on an end wall of it, which is located opposite the end wall adjacent to the inlet space of the housing.
The problem underlying the invention is to provide an arrangement for the separation of fiber suspensions which are heavily laden with contaminants, especially for an end-stage sorting. By "end-stage sorting" is meant the process step in which the collected reject shares of the individual sorting stages are to be cleaned once again in order to reclaim usable fibers. Such a machine would then be able to additionally clean suspensions with a medium-heavy content of contaminants.